The long term goal of this proposal is to understand the mechanisms by which the mu opioid receptor (Oprm) gene is regulated and to gain insights into the pharmacological and physiological significance of this regulation. Early pharmacological studies have proposed several mu opioid receptor subtypes: mu1, mu2 and morphine-62-glucuronide (M6G). However, only one mu opioid receptor gene has been identified, raising the possibility that alternative pre-mRNA splicing and multiple promoters of the Oprm gene may be responsible for the multiple mu opioid receptors. Over the last ten years, we have identified 25 splice variants from the mouse Oprm gene, 13 splice variants from the rat Oprm gene and 12 from the human Oprm gene. The functional significance of the splice variants is supported by differences in regional and cell-specific expression, agonist-induced G protein coupling and receptor internalization. Diversity of the Oprm gene was further demonstrated by isolation of a new promoter, exon 11 promoter (E11 promoter). Conservation of the E11-associated variants and the E11 promoter has also been confirmed by identifying these mouse homologs in the rat and human Oprm genes. Our recent knockin/knockout study showed that in mice lacking exon 11, M6G, 6-acetylmorphine and heroin analgesia were greatly diminished, while morphine's response remained unchanged, implying a major functional role for exon 11-associated splice variants and exon 11 promoter in mediating the actions of a subset of mu opioids. This proposal will continue to explore the regulations and functions of E11 promoters by proposing the following specific aims: 1). To characterize the mouse E11 promoter; 2). To investigate structure and function of the human E11 promoter; 3). To explore the pharmacological function of E11 and E1 promoters using double gene targeting mouse model. The knowledge gained from this proposal will help us obtain a better understanding of the complexity and functional importance of Oprm gene regulation, establish the gene targeted animal models for studying the underlying mechanisms of this gene regulation and function, and provide potential targets for developing novel drugs used in control of pain and drug of abuse. The primary goal of this proposal is to further investigate the regulations and functions of a new promoter, exon 11 promoter, in the mu opioid receptor (Oprm) gene. The knowledge gained from this proposal will help us obtain a better understanding of the complexity and functional importance of Oprm gene regulation, establish the gene targeted animal models for studying the underlying mechanisms of this gene regulation and function, and provide potential targets for developing novel drugs used in control of pain and drug of abuse.